1. Field of the Invention
The present invention relates to a camera shake correction system and, in particular, to such camera shake correction system which combines an electronic camera shake correction means and a mechanical camera shake correction system.
2. Description of the Related Art
Conventionally, there has been known an electronic camera shake correction system which processes a picture image obtained from an image pickup means in a digital signal to thereby correct the amount of movement of a screen. In this type of electronic camera shake correction system, the predetermined areas of image data between fields are compared with each other to find a mutual relation therebetween to thereby detect the amount of parallel movement of a following image with respect to a leading image, and the image to be output is shifted by the thus detected amount of parallel movement in the opposite direction (Japanese Patent Publication (Tokkai) No. 1-109970).
On the other hand, as a mechanical camera shake correction system, there has been known a system in which there is inclinably arranged a correction mirror having an angle of about 45.degree. with respect to the optical axis of a taking lens, and the correction mirror is driven to stabilize the light of an object incident onto an image pickup surface through the correction mirror and taking lens, or a system in which the whole of a taking lens or at least one of a plurality of lenses forming the taking lens is inclinably supported by a gimbal mechanism or the like, and the supported lens is driven to stabilize the object light incident onto the image pickup surface.
Also, as an angular velocity sensor which can be used in this type of mechanical camera shake correction system to detect the shake of a camera, there is generally known a sensor which utilizes a Coriolis force. This angular velocity sensor outputs a voltage signal proportional to an angular velocity. However, in this angular velocity sensor, in order to obtain an absolute angular velocity, it is necessary to detect an output value obtained at the time when the angular velocity is 0 (that is, the central value voltage of the sensor) and then to subtract the central value voltage from the sensor output.
Referring back to the above-mentioned conventional electronic camera shake correction system, it is inexpensive because it does not use any mechanical sensor such as an angular velocity sensor or the like. Also, since the correction system employs a signal post-process method using a field memory, it is free from delay and is able to correct the camera shake with high accuracy. However, due to the fact that a picture having a predetermined size but smaller than an input picture is cut out from the input picture according to the detected amount of parallel movement and the thus cut screen is then enlarged up to the same size of the input picture before it is output, the number of effective pixels is reduced. For this reason, according to the conventional electronic camera shake correction system, in order to prevent the deterioration of picture quality due to such reduction of the number of the effective pixels, the size of the picture to be cut out is normally limited to the order of 90% of the input picture, with the result that the correction can be made only within a range of 10% or so with respect to the input picture. This means that the limit of the camera shake correction is 1.degree. if a picture angle in photographing is, for example, 10.degree., that is, a sufficient camera shake correction effect cannot be achieved.
Also, when an angular velocity sensor is used, as a method of detecting the output value obtained when the angular velocity of the angular velocity sensor is 0, there have been proposed several methods. In one of them, the average value of the sensor outputs for a long period of time is calculated to thereby detect the above-mentioned output value. In another one of them, the variations of the angular velocity are followed, a stationary state is checked according to the characteristics of the angular velocity variations, and the above-mentioned output value is detected from the then output value. However, because all of the methods are based on the output of the angular velocity sensor, there is the possibility of mis-detection. Also, there is known the fact that the sensor outpull of the angular velocity sensor includes a drift component which has no connection with the angular velocity, and this drift component makes it difficult to detect the angular velocity with accuracy.
Also, conventionally, there has never been proposed such camera shake correction system that combines an electronic camera shake correction device with a mechanical camera shake correction device. None of the conventional camera shake correction systems can distinguish the panning operation or tilting operation of a camera from the operation of following an object. As a result of this, the camera shake correction is executed without confirming which of the operations is required and, therefore, an unnatural picture is inevitably produced. For example, if the camera is panned while the electronic camera shake correction system is kept operable, then the picture is stopped within a range that can be corrected by the electronic camera shake correction system, and if the correctable range is over, then the picture is instantaneously moved and is stopped again; such moving and stopping motions are repeated to provide an intermittently moving picture. On the other hand, if the camera is panned while the mechanical camera shake correction system is kept operable, then the camera shake correction is limited by the movable range of the optical members of the mechanical camera shake correction system; that is, the picture is stopped only in the early panning operation, and after then, the shake correction is possible only in one direction because the optical members are brought into contact with a mechanical stopper.
Therefore, in order to avoid the above-mentioned unnatural picture, a photographer must judge the above-mentioned photographing conditions and remove the camera shake correction, which provides a complicated operation.
Further, the mechanical camera shake correction system uses an angular velocity sensor utilizing a Coriolis force. This angular velocity sensor is not able to detect a small angular velocity (1.degree./sec. or smaller) because the Coriolis force of the sensor itself is small and, therefore, the angular velocity sensor is not able to correct a small angular velocity movement (that is, a slow movement). On the other hand, when the amount of the movement of the picture is detected from the image data in the electronic camera shake correction system, a slight angular velocity can be detected but a large angular velocity cannot be detected.